This invention relates to a vehicle, such as a refuse truck, having an internal combustion engine and an electric motor in parallel, meaning that either or both of the engine and motor can drive the vehicle's transmission.
Hybrid vehicles typically use two types of stored energy: chemical and electrical. An internal combustion engine (ICE) in a hybrid vehicle converts chemical energy into mechanical energy in the combustion chambers. An electric motor in the hybrid vehicle converts stored electrical energy into mechanical energy.
In some hybrid vehicles, the electric motors supplement the ICEs, which is to say that the electric motors supply driving torque to assist the ICEs. Such hybrid vehicles are sometimes called “parallel hybrids”. Other hybrid vehicles are driven by the electric motors, with the ICEs driving generators that charge batteries or other electric energy storage devices. Such hybrid vehicles are sometimes called “series hybrids”.
A parallel hybrid vehicle thus usually includes an ICE, an electric motor, and a transmission, drive shaft, axle carrier, axle, and wheels, all of which are arranged in series to transmit torque from the ICE and motor to the wheels. Such a hybrid vehicle can be operated by either the engine only, or the motor only, or the engine and motor together. The electric motor may be operated as an electric generator during deceleration of such a vehicle to recover some of the vehicle's kinetic energy.
Typical hybrid vehicles, such as that described in U.S. Pat. No. 5,984,033 to Tamagawa et al., size the ICE to meet average power demands and size the electric motor to meet peak power demands. Of course, such designs are not optimal for every vehicle application, in particular delivery and pick-up applications which involve frequent starts and stops. In such applications, careful management of the energy expended during acceleration and the energy regenerated during deceleration is necessary for optimal vehicle efficiency.
U.S. Pat. No. 5,942,879 to Ibaraki discloses a hybrid vehicle that uses an electric motor as a generator and vehicle braking device. Recovered energy is managed for controlling a battery's state of charge. During deceleration regeneration, an optimal rotation speed at which the regeneration output of the motor/generator becomes maximal is determined, and the vehicle's transmission gear ratio is controlled such that the rotation speed of the motor/generator is the calculated optimum speed.
U.S. Pat. No. 5,875,864 to Yano et al. discloses calculating an amount of regenerated energy that can be captured during engine deceleration for use in controlling recharge of a battery array. The patent discusses opening an engine intake air valve to reduce engine retarding torque, allowing the motor/generator to capture more energy from slowing the vehicle.
U.S. Pat. No. 6,523,626 to Wakashiro et al. discloses a control device for a hybrid vehicle that monitors the depth of discharge of a storage unit, in particular a capacitor, and recharges the capacitor using regenerative braking or engine output when the depth-of-discharge exceeds a threshold.
U.S. Pat. No. 6,945,905 to Tamai et al. discloses methods of monitoring the state of charge of a battery in a hybrid vehicle and selecting a gear ratio so that a motor/generator produces a desired level of regenerated braking energy.
U.S. Patent Application Publication No. 2004/0204797 by Vickers describes an apparatus for regulating the engine in a hybrid vehicle. A circuit computes a distance from the vehicle to a predetermined destination and senses an amount of energy in an electric storage cell. The circuit regulates the engine as a function of the distance and the amount of energy, giving the vehicle operator the option of arriving with low charge and using an electric outlet for charging, or using engine or braking regeneration on the way for recharging.
These and other prior approaches to energy management in hybrid vehicles still suffer from drawbacks in various vehicle applications, such as delivery and pick-up applications.